Dr. Universe: Back when cell phones weren’t a thing, how could you place a call from across the ocean? Were there wires under the ocean? -Tali, 9, Seattle, Wash.

Long before telephones, if you wanted to say “hi” to friend across the ocean you’d probably write them a letter and send it over on a ship.

But in the last hundred years or so, we’ve been able to connect across the ocean much faster. And yes, it often required thousands of miles of wires, or cables, deep in the sea.

That’s what I found out from my friend Bob Olsen, a professor of electrical engineering at Washington State University, who told me all about the telephone.

The telephone helps translate the sound waves from your voice into electrical signals. Those electrical signals can flow through cables on land and, as you hypothesized, under the ocean.

The era of the landline

Before there were cell phones, we made calls on a landline. It was a kind of phone with copper wires that flowed from your phone, into the wall, and onto a phone company’s central office.

When you’d dial a long-distance number, a lot of things started happening behind the scenes.

After you dialed the number, someone at the phone company’s central office would get your call. At the office, that person would help switch the call, or move the right wires around, to connect you with their long-distance office.

The person at the long-distance office would connect your call to the phone company office nearest to your friend’s house. The wires on land and the cables beneath the ocean helped this message travel in the form of electrical signals.

Wires and satellites

While we used to depend on people to help make the switches, now computers can do it. As engineers came up with new ideas about telephones, they also learned they could use satellites to help these signals travel long-distances. Instead of using long-distance cables, a call goes up to a satellite and bounces back down to your friend.

Olsen said he remembers calling his uncle who lived across the country once a year. It was a special occasion and all of the kids in his family would line up to just say “hello.” It was very expensive to make a long-distance call. Maybe you can ask your parents or grandparents about it.

Speedy signals

Even though a lot of people now use wireless phones rather than landlines to connect with each other, we still depend on those wires under the ocean for long-distance phone calls. The old wires have now been replaced with optical fibers that are a much better way to send these signals. We also depend on them for one big thing many of us use every day: Internet.

When we search the web, make a video call, or send texts from an app overseas, that information in the form of electrical signals is flowing deep beneath the ocean on optical fiber cables. You can check out this map to see how the cables work and are all connected.

The next time I go to the ocean or call a friend, I’m going to remember the important work electrical engineers to do help us all stay connected—and let me answer great questions from kids like you.